"ZZ Top was the best band in the world at remaining mysterious for so long. That was part of their appeal. You saw these beards, and they didn’t talk as much as they do these days. There was just a real mystery about them for a long time. And then in terms of their sound, I always liked people who are unique, and nobody ever sounded like them, before or since. You can call it blues rock or whatever, but once you hear the guitar of Billy Gibbo...